Why severe coronavirus causes more damage than typical pneumonia

Alexandra Thompson
·3 min read
Ventilator monitor ,given oxygen by intubation tube to patient, setting in ICU/Emergency room
Severe coronavirus' slower disease course may trigger more tissue damage than typical pneumonia. (Posed by a model, Getty Images)

A study appears to have shed light on why severe coronavirus cases cause more lung damage than typical pneumonia.

Early in the pandemic, pneumonia emerged as a leading cause of death among critically-ill patients.

Although often triggered by specific bacteria, pneumonia can occur if any infection spreads to the air sacs in the lungs, making them inflamed and filled with fluid. This dampens gas exchange, causing oxygen levels in the blood to fall and carbon dioxide to accumulate.

The responsible infections tend to spread across large areas of the lungs over several hours, but can often be fought off naturally or with antibiotics.

When it comes to the coronavirus, scientists from Northwestern University discovered the infection sets up shop in a small region of the lungs. It then hijacks immune cells, using them to spread across the organ over many days or even weeks.

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As the coronavirus slowly moves across the lung, it is said to leave tissue damage in its wake.

The coronavirus may be more damaging than typical pneumonia due to the longer course of the disease, rather than it causing more severe illness, according to the scientists.

Unable to marshal the right cells and molecules to fight off the invader, the bodies of the infected instead launch an entire arsenal of weapons — a misguided barrage that can wreak havoc on healthy tissues, experts said. (Getty Images)
The coronavirus appears to hijack immune cells, using them to move across a patient's lungs. (Stock, Getty Images)

Early in the pandemic, the scientists collected fluid from the lungs of 88 severe coronavirus patients.

These samples were compared against fluid collected before the coronavirus outbreak from 211 individuals in intensive care with pneumonia.

The scientists analysed the coronavirus samples’ genetic material and protein expression, enabling them to identify how it hijacks immune cells to drive inflammation.

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Perhaps surprisingly, reports have emerged that coronavirus patients on ventilators have a lower mortality rate than when individuals with typical pneumonia are treated this way.

In a second part of the investigation, the Northwestern scientists analysed the lung fluid of 86 coronavirus patients on a ventilator and 256 individuals on a ventilator with another type of pneumonia.

Results – published in the journal Nature – suggest coronavirus-related pneumonia causes less severe lung inflammation, despite it lasting for longer.

“If patients with COVID-19 [the disease caused by the coronavirus] are carefully managed and the health care system isn’t overwhelmed, you can get them through it,” said study author Dr Scott Budinger.

“These patients are very sick. It takes a really long time for them to get better.

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“But if you have enough beds and healthcare providers, you can keep the mortality to 20%.

“When health systems are overwhelmed mortality rates double up to 40%.”

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The scientists found targeting immune cells called macrophages and T-cells could treat severe coronavirus-related pneumonia, lessening its damage.

They plan to test an experimental drug that targets these cells in coronavirus-pneumonia patients in early 2021.

“Our goal is to make COVID-19 mild instead of severe, making it comparable to a bad cold,” said Dr Budinger.

The experimental drug is hoped to dampen the immune cells’ inflammatory response, enabling injured lung tissue to be repaired.

Like seasonal flu, many experts do not expect the coronavirus to go away, even if the majority of the population is vaccinated.

“Already, researchers at Northwestern and elsewhere are anticipating mechanisms by which this RNA virus, which mutates quickly, will evade current vaccines,” said co-author Dr Ben Singer.

“This study will help us develop treatments to reduce the severity of COVID-19 in those who develop it.”

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